For all that history teachers appreciate the need to build substantive knowledge and conceptual understanding systematically over time, they are also likely to have experienced that sickening moment when they realise that a Year 11 pupil has somehow missed something fundamental. In Anna Fielding's case, her pupil's misconception was related to the process of change, which was to feature as "the" most important second-order concept within their final GCSE module. Resisting the temptation to panic, but nonetheless working under tight time pressure, Fielding set out to first to examine and then to reconstruct her pupils' ideas. The tightly-planned sequence of lessons that she outlines and discusses in this article demonstrates the way in which she drew on insights from other teachers' classroom research in combination with her own systematic analysis of her pupils' urgent needs to transform their capacity to write analytically about the process of change.